Junction between a microstrip line and a waveguide

ABSTRACT

An arrangement for a junction between a microstripline and a waveguide is provided. The arrangement includes a microstripline fitted on the upper face of a dielectric substrate, a waveguide fitted on the upper face of the substrate and has an opening on at least one end surface and has a structure which is in the form of a step or steps in the area of the opening on one side wall and is conductively connected in at least one part to a microstripline. One side wall of the waveguide is a metallized layer formed on the substrate. A cutout is formed in the metallized layer and into which the microstripline projects. A rear-face metallization is formed on the rear face of the substrate, and electrically conductive via holes between the metallized layer on the upper face of the substrate and the rear-face metallization, which surround the cutout.

BACKGROUND AND SUMMARY OF THE INVENTION

In many extra-high frequency technology applications, in particular formillimetric wave technology, it is necessary to inject a wave which hasbeen carried in a microstripline into a waveguide, and vice versa. Inthis case, the junction should be as free of reflections and losses aspossible. This junction ensures, within a limited frequency range, thatthe impedances between the waveguide and the stripline are matched toone another, and that the field pattern of the first waveguide type istransferred to the field pattern of the other waveguide type.

Microstripline/waveguide junctions are known, for example, from DE 19741 944 A1 or U.S. Pat. No. 6,265,950 B1.

DE 197 41 944 A1 describes an arrangement in which the microstripline isapplied to the upper face of the substrate (FIG. 1). An end surface ofthe waveguide HL is fitted on the lower face of the substrate S. Thesubstrate S has an aperture D in the area of the waveguide HL, whichaperture D corresponds essentially to the cross section of the waveguideHL. A coupling element (not illustrated) is arranged on themicrostripline ML and projects into the aperture D. The aperture D issurrounded on the upper face of the substrate S by a screening cap SK,which is electrically conductively connected by means of electricallyconductive drilled holes (via holes) VH to the metallization RM on thelower face of the substrate S.

This arrangement has the disadvantage that the printed circuit boardmust be mounted conductively on a prepared mounting plate containing thewaveguide HL. In addition, a precision manufactured shielding cap SK,which is mechanically positioned with precision and must be appliedconductively, is required. The production of this arrangement istime-consuming and costly owing to the large number of different typesof processing steps. Further disadvantages result from the large amountof space required as a result of the waveguide being arranged outsidethe printed circuit board.

In the arrangement described in U.S. Pat. No. 6,265,950 B1 for ajunction between a microstripline and a waveguide, the substrate withthe microstripline applied to it projects into the waveguide. Onedisadvantage of this arrangement is the integration of the waveguide ina printed circuit board environment. The waveguide can be arranged onlyon the boundary surfaces of the printed circuit board (substrate). Thewaveguide cannot be integrated within the printed circuit board, becauseof the costly preparation of the printed circuit board.

The object of the invention is to specify an arrangement for a junctionbetween a microstripline and a waveguide, which can be produced easilyand at low cost and which occupies only a small amount of space.

The arrangement according to the invention for a junction between amicrostripline and a waveguide comprises:

-   -   a microstripline which is fitted on the upper face of a        dielectric substrate,    -   a waveguide which is fitted on the upper face of the substrate        and has an opening on at least one end surface and has a        structure which is in the form of a step or steps in the area of        the opening on one side wall and is conductively connected in at        least one part to the microstripline, and wherein one side wall        of the waveguide is a metallized layer formed on the substrate,    -   a cutout which is formed in the metallized layer and into which        the microstripline projects,    -   rear-face metallization which is formed on the rear face of the        substrate, and    -   electrically conductive via holes between the metallized layer        on the upper face of the substrate and the rear-face        metallization, which surround the cutout.

One advantage of the arrangement according to the invention is that themicrostrip/waveguide junction can be produced easily and at low cost.The production of the junction requires fewer components than the priorart. A further advantage is that the implementation of the waveguide inthe printed circuit board environment need not be at the edge of theprinted circuit board as in the case of the U.S. Pat. No. 6,265,950 butcan be provided at any desired point on the printed circuit board. Thearrangement according to the invention thus occupies little space.

The waveguide is advantageously a surface mounted device. The waveguidepart is for this purpose fitted to and conductively connected to theprinted circuit board from above in a single fitting step. Theconnection of the waveguide to the junction can thus be integrated inknown component placement methods. This saves manufacturing steps, thusreducing the production costs and time.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

The invention as well as further advantageous refinements of thearrangement according to the invention will be explained in more detailin the following text with reference to the drawings, in which:

FIG. 1 shows a longitudinal section through an arrangement for amicrostrip/waveguide junction according to the prior art,

FIG. 2 shows a plan view of the metallized layer on the upper face ofthe substrate,

FIG. 3 shows a perspective view of an example of an internal structure,which is in the form of a step or steps, for the surface mounted device,

FIG. 4 shows a longitudinal section through an arrangement according tothe invention for a microstrip/waveguide junction,

FIG. 5 shows a first cross section through the area 3 in FIG. 4,

FIG. 6 shows a second cross section through the area 4 in FIG. 4,

FIG. 7 shows a third cross section through the area 5 in FIG. 4,

FIG. 8 shows a fourth cross section through the area 6 in FIG. 4, and

FIG. 9 shows a further advantageous embodiment of themicrostrip/waveguide junction according to the invention.

DETAILED DESCRIPTION

FIG. 2 shows a plan view of the metallized layer of the substrate. Thismetallized layer is also referred to as a land structure for themicrostrip/waveguide junction. The land structure LS has a cutout A withan opening OZ. The microstripline ML runs through this opening OZ andends within the cutout A. The cutout A is surrounded by via holes VH.These via holes VH are electrically conductive apertures in thesubstrate, connecting the land structure LS to the rear-facemetallization (not illustrated) on the rear face of the substrate. Thedistance between the via holes VH is chosen to be sufficiently shortthat the radiated emission of the electromagnetic wave through theintermediate spaces is small within the useful frequency range. The viaholes VH may in this case advantageously also run in a number of rows,which are arranged parallel to one another, in order to reduce theradiated emission.

FIG. 3 shows a perspective illustration of an example of an internalstructure, which is in the form of a step or steps, for the surfacemounted device. The component B likewise has an opening OB,corresponding to the opening in the cutout in the land structure (seeFIG. 2). A structure ST1, ST, which is in the form of a step or steps orsteps, is formed in the longitudinal direction of the component, at adistance which can be predetermined from the opening OB on the sidewall. That side wall of the component B which contains the steppedstructure ST1 and ST is opposite the substrate surface afterinstallation of the land structure LS (see FIG. 4). The waveguidecomponent B to be fitted is open at the bottom (in the direction of thesubstrate) before being fitted, and is thus still incomplete. The sidewall which is still missing is formed by the land structure LS on thesubstrate.

The arrangement according to the invention is, furthermore, notrestricted by the number of steps illustrated in FIG. 3 or FIG. 4. Thenumber, length and width of the individual steps in the structure ST canbe matched to the respective requirements of the junction. It is, ofcourse, also possible to provide a continuous junction.

In the illustration shown, the step annotated with the reference symbolST1 is of such a height that, when the component B is fitted to the landstructure as shown in FIG. 2 in an interlocking manner, the step ST1rests directly on the microstripline ML, thus making an electricallyconductive connection between the microstropline ML and the component B.

FIG. 4 shows a longitudinal section through an arrangement according tothe invention of a microstrip/waveguide junction. In this case, thecomponent B as shown in FIG. 3 is fitted in an interlocking manner tothe land structure of the substrate S as shown in FIG. 3. The componentB is in this case fitted, in particular, to the substrate in such a waythat an electrically conductive connection is made between the landstructure and the component B.

On the lower face, the substrate S has an essentially continuousmetallic coating RM. The waveguide area is annotated with the referencesymbol HB in the illustration. The junction area is annotated with thereference symbol UB.

The microstrip/waveguide junction according to the invention operates onthe following principle: the radio-frequency signal outside thewaveguide HL is passed through a microstripline ML with the impedance Z₀(area 1). The radio-frequency signal within the waveguide HL is carriedin the form of the TE1o basic waveguide mode. The junction UB convertsthe field pattern of the microstrip mode in steps to the field patternof the waveguide mode. At the same time, by virtue of the steps in thecomponent B the junction UB transforms the characteristic impedance andensures that the impedance Z₀ is matched, within the useful frequencyrange, to the impedance Z_(HL) of the waveguide HL. This allows alow-loss and low-reflection junction between the two waveguides.

First of all, the microstripline ML leads into the area 2 of a so-calledcutoff channel. This channel is formed from the component B, therear-face metallization RM and the via holes VH, which create aconductive connection between the component B and the rear-facemetallization RM. The width of the cutoff channel is chosen such that noadditional wave type other than the signal-carrying microstrip mode canpropagate in this area 2. The length of the channel determines theattenuation of the undesirable waveguide mode which cannot propagate,and prevents radiated emissions into free space (area 1).

In the area 3, the microstripline ML is located in a type of partiallyfilled waveguide. The waveguide is formed from the component B, therear-face metallization RM and the via holes VH (FIG. 5). The structureof the component B, which is in the form of a step or steps or steps, isconnected in the area 4 to the microstripline ML (FIG. 6). The sidewalls of the component B are conductively connected to the rear facemetallization RM of the substrate S by means of a socalled shielding rowof via holes VH.

This results in the formation of a dielectrically loaded ridgewaveguide. The signal energy is concentrated between the rear-facemetallization RM and the ridge which is formed from the microstriplineML and that of the step ST1 of the component B.

In comparison to the area 4, the height of the stepped structure STcontained in the component B decreases in the area 5, so that a definedair gap L is formed between the substrate material and the steppedstructure ST when the component B is connected in an interlocking mannerto the land structure LS on the substrate S (FIG. 7). The side walls ofthe component B are conductively connected to the rear-facemetallization RM through via holes VH. This results in a partiallyfilled, dielectrically loaded ridge waveguide.

The width of the step widens for the purpose of gradually matching thefield pattern from area 4 to the field pattern of the waveguide mode(area 6). The length, width and height of the steps are chosen such thatthe impedance of the microstrip mode Zo is transformed to the impedanceof the waveguide mode ZHL at the end of the area 6. If required, thenumber of steps in the structure of the component B in the area 5 canalso be increased, or a continuously tapered ridge may be used.

The area 6 illustrates the waveguide area HB. The component B forms theside walls and the cover of the waveguide HL. The waveguide base isformed by the land structure LS on the substrate S, that is to say, incomparison to the area 5, there is now no dielectric filling in thewaveguide HL.

One or more shielding rows of via holes VH in the junction area betweenthe area 5 and the area 6, which run transversely with respect to thepropagation direction of the wave in the waveguide, provide the junctionbetween the partially dielectrically filled waveguide and the purelyair-filled waveguide. At the same time, these shielding rows prevent thesignal from being injected between the land structure LS and therear-face metallization.

A stepped structure (analogous to the stepped structure in the area 5)can optionally also be provided in the area 6 in the cap upper part.

The length and height of these steps is chosen analogously to the area5, so that, in combination with the other areas, the impedance of themicrostrip mode Z₀ is transformed to the impedance Z_(HL) for thewaveguide mode at the end of the area 6.

FIG. 9 shows a further advantageous embodiment of themicrostrip/waveguide junction according to the invention. Thisembodiment makes it possible to provide a simple and low-cost waveguidejunction in which the radio-frequency signal can be output through thesubstrate 6 downwards through the continuous waveguide opening DB whichis contained in the substrate. The waveguide opening DB advantageouslyhas electrically conductive internal walls (IW). The component Badvantageously has a stepped shape ST in the area of the aperture DB onthe side wall opposite the waveguide opening DB. This stepped shape STdeflects the wave in the waveguide through 90° from the waveguide areaHB of the component B into the waveguide opening DB in the substrate S.A further waveguide or a radiating element, for example, can be arrangedon the lower face of the substrate S, in the area of the waveguideopening DB. In the present example shown in FIG. 9, a further supportmaterial TP, for example a printed circuit board having one or morelayers or a metal mount, is fitted to the rear-face metallization RM. Incomparison to DE 197 41 944 A1, the advantage of this arrangement is thesimplified, more cost-effective design of the substrate S and of thesupport material TP. The waveguide opening is milled all the waythrough, and the internal walls are electrochemically metallized. Bothprocess steps are standard processes which are normally used in printedcircuit board technology and can be carried out easily.

1-8. (canceled)
 9. An arrangement for a junction between amicrostripline and a waveguide, comprising: a microstripline which isfitted on an upper face of a dielectric substrate; a waveguide which isfitted on the upper face of the substrate and has an opening on at leastone end surface and has a structure which is in the form of a step orsteps in the area of the opening on one side wall and is conductivelyconnected in at least one part to the microstripline, and wherein oneside wall of the waveguide is a metallized layer formed on thesubstrate; a cutout which is formed in the metallized layer and intowhich the microstripline projects; rear-face metallization which isformed on a rear face of the substrate; and electrically conductive viaholes between the metallized layer on the upper face of the substrateand the rear-face metallization, which surround the cutout.
 10. Thearrangement as claimed in claim 9, wherein the waveguide is a surfacemounted device.
 11. The arrangement as claimed in claim 9, wherein thestructure which is in the form of a step or steps is formed on a sidewall of the waveguide which is opposite the cutout.
 12. The arrangementas claimed in claim 10, wherein the structure which is in the form of astep or steps is formed on a side wall of the waveguide which isopposite the cutout.
 13. The arrangement as claimed in claim 9, whereina distance between the via holes is chosen such that the radiatedemission of the electromagnetic wave in the useful frequency rangethrough the intermediate spaces is small, and the operation of thejunction is thus not adversely affected by increased losses orundesirable couplings.
 14. The arrangement as claimed in claim 13,wherein the via holes run in a number of rows which are arrangedparallel to one another.
 15. The arrangement as claimed in claim 9,wherein the substrate has a waveguide opening in the area of themetallized layer on the upper face of the substrate.
 16. The arrangementas claimed in claim 11, wherein the substrate has a waveguide opening inthe area of the metallized layer on the upper face of the substrate. 17.The arrangement as claimed in claim 14, wherein an inner surface of thewaveguide opening is electrically conductive.
 18. The arrangement asclaimed in claim 14, wherein a side wall of the waveguide which isopposite the upper face of the substrate has a structure, which is inthe form of a step or steps, in the area of the waveguide opening. 19.The arrangement as claimed in claim 15, wherein a side wall of thewaveguide which is opposite the upper face of the substrate has astructure, which is in the form of a step or steps, in the area of thewaveguide opening.